Photoreactions indicate the general chemical reactions that lead to absorption of energy into molecules (i.e., radical reactant) by light irradiation to excite the molecules to a higher energy level (i.e., to the excited state) and initiate a reaction with the excited molecules. Photoreaction is also called photochemical reaction. According to “Kagaku Jiten,” pages 457-458, Tokyo Kagaku Dojin, photoreactions include oxidation and reduction reactions with light and substitution and addition reactions with light. It is known that photoreactions have a variety of applications including not only photographic industries, photocopying technology, induction of photovoltaic power, but syntheses of organic compounds. Photochemical smog is also one type of photochemical reaction or more specifically unintentional photochemical reaction.
As described in JP 2010-6775 A and Journal of the Japan Petroleum Institute, Vol. 17, No. 10 (1974), pages 72-76, there is a known technique of synthesizing cyclohexanone oxime by the photochemical reaction. It is also known that the wavelength of 400 to 760 nm is desirable as the effective wavelength for the reactions of a cycloalkanone oxime. Examples of the light emitter having the energy output characteristics specialized in such a specific wavelength range include light sources such as light emitting diodes, lasers and organic electroluminescence (organic EL).
Light emitting diodes have the advantage of directly converting electrical energy into light by using a semiconductor. Light emitting diodes have drawn attention because of, for example, the less heat generation, efficient use of energy and the long life. In the recent years, LEDs of high efficiency and high output have been developed. As a result, this allows for replacement of incandescent lamps and fluorescent lamps with LEDs in general lighting use. In industrial use, LEDs are expected to achieve a practical level in some years.
In such environments, a production method of a cycloalkanone oxime having the following characteristics has been proposed in JP '775: (i) in the emission energy distribution with respect to the wavelength of the light source, it is desirable that the emission energy in the wavelength range of less than the wavelength of 400 nm is equal to or less than 5% of the maximum value of emission energy and that the emission energy in the wavelength range of greater than the wavelength of 760 nm is equal to or less than 5% of the maximum value of emission energy; (ii) the light emitting diodes used are those having the energy conversion efficiency equal to or greater than 3%; and (iii) a plurality of light emitting diodes arrayed in a plane along the side face of a photochemical reactor containing a photoreaction liquid are used to irradiate the photochemical liquid with light via the permeable photochemical reactor.
Additionally, the technique disclosed in JP 2010-6776 A synthesizes cyclohexanone oxime under the following conditions. Light emitting diodes are used as the light source. In the emission energy distribution with respect to the wavelength of the light source, a wavelength providing a maximum value of emission energy is 400 nm to 760 nm. A cooling jacket is provided on the rear surface of the light source, and a cooling medium is continuously introduced into the cooling jacket to forcibly and indirectly cool down the light source. In the emission energy distribution with respect to the wavelength of the light source, the wavelength providing the maximum value of emission energy is 430 nm to 650 nm. The integrated value of emission energy in the wavelength range of 400 nm to 760 nm relative to the emission energy in the wavelength range of 300 nm to 830 nm is equal to or greater than 95%. JP '776 also includes the descriptions on the temperature of the cooling medium introduced into the cooling jacket, the method of arraying the light emitting diodes, and the minimum distance of irradiation between the light emitting diodes and the side face of the photochemical reactor.
Furthermore, the technique disclosed in JP 2011-521004 A performs photonitrosation of a cycloalkanone oxime in a very narrow space with a microreactor using light emitting diodes.
Selectivity in the methods described in the above publications, i.e., a production ratio of a target component to a “raw material converted by the reaction,” is not clearly specified. In the phase of industrialization, there is a need to improve the selectivity, i.e., setting the conditions to obtain a target product more efficiently.
It could therefore be helpful to maximize selectivity to reduce the amount of a raw material used in the phase of industrialization, while maintaining the production amount of a reaction product per input amount of electric power in the photonitrosation method using a light source having a narrow wavelength distribution.